1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus, a control method therefor, and a computer-readable storage medium storing a control program for implementing the control method, and in particular to a solid-state image pickup apparatus having analog-to-digital converters in respective columns.
2. Description of the Related Art
In general, an image obtained by shooting in a case where there is an object (subject) with high brightness such as a headlight or sunlight within a shooting area is required to have no so-called blown out highlights and also required to have no blocked up shadows in a low-brightness range. Namely, at the time of shooting, an image with wide dynamic range is required.
To obtain an image with wide dynamic range, first, a low-sensitivity image suitable for a subject with a high brightness and a high-sensitivity image suitable for a subject with a low brightness are obtained. The images of these two types are subjected to image processing to generate an image with wide dynamic range. Accordingly, solid-state image pickup apparatuses such as CMOS image sensors capable of obtaining a low-sensitivity image and a high-sensitivity image are needed.
Additionally, in general, progressive moving images of 30 Hz and interlace moving images of 60 Hz have been conventionally used as moving images, and with speed-up of a display device, solid-state image pickup apparatuses capable of taking progressive moving images of 60 Hz and images at high frame rate not less than 60 Hz have been required.
If images can be taken at high frame rate, motions of a subject moving at high speed can be accurately captured. If a solid-state image pickup apparatuses capable of taking images at high frame rate is used, a plurality of images can be synthesized to enable image processing such as improvement of the S/N ratio and enlargement of dynamic range.
There have been solid-state image pickup apparatuses in which two or more analog-to-digital converters (ADC) are provided in each pixel column, and outputs from a plurality of pixels in a pixel column are allocated to these ADCS, so that speed can be increased by parallel processing (see Japanese Laid-Open Patent Publication (Kokai) No. 2005-347932).
There have also been solid-state image pickup apparatuses in which a unit pixel has a first photodiode that photoelectrically converts incident light and accumulates the same and a second photodiode with lower sensitivity to light as compared to the first photodiode. Here, when signal electric charges in the first and second photodiodes are to be read out, there are a high-sensitivity mode in which a signal obtained by amplifying a potential obtained by reading out and adding up the signal electric charges together is output, and a low-sensitivity mode in which a potential obtained by amplifying a potential obtained by reading the signal electric charges in the second photodiode is output (see Japanese Laid-Open Patent Publication (Kokai) No. 2011-15219). As a result, when the amount of incident light is small, sensitivity is increased, and when the amount of incident light is large, sensitivity is decreased so that saturation of outputs can be avoided to widen dynamic range.
Further, there have been solid-state image pickup apparatuses which, in order to enlarge dynamic range, have a plurality of split pixels obtained by dividing one pixel in a pixel unit, in which a plurality of pixels is arranged in a matrix, into areas in which electric charges in different amounts are accumulated, and at the time of reading pixel signals, read out split pixel signals of the respective split pixels, subject the split pixel signals to A/D conversion, and add them up to obtain a pixel signal of one pixel (see Japanese Laid-Open Patent Publication (Kokai) No. 2010-28423).
As described above, Japanese Laid-Open Patent Publication (Kokai) No. 2005-347932 describes the method for taking images at high frame rate, and Japanese Laid-Open Patent Publication (Kokai) No. 2011-15219 and Japanese Laid-Open Patent Publication (Kokai) No. 2010-28423 describe the method for enlarging dynamic range, but they do not mention taking of images at high frame rate while enlarging dynamic range.
In particular, when one pixel has a plurality of photodiodes as with the method described in Japanese Laid-Open Patent Publication (Kokai) No. 2011-15219 and Japanese Laid-Open Patent Publication (Kokai) No. 2010-28423, it is difficult to read out pixel signals at high frame rate.